In the motor vehicle drive trains known from the state of the art, which are equipped respectively with an internal combustion engine, a transmission device and an output. The component assemblies thereof are subjected to stresses depending on operating state. These stresses result from the greater frictional stresses on switching elements that are periodically operated in a slipping state during startup procedures or switching operations in the transmission device.
In order to reduce fuel consumption and pollutant emissions, motor vehicles are increasingly equipped with hybrid drives. In motor vehicles, systems are provided with both parallel and serial arrangement of the two drive systems, that is, the internal combustion engine and the electric engine.
When there is parallel arrangement of the two drive systems, a vehicle can be operated by both drives independent of each other, where an internal combustion engine can be separated from an electric engine by way of a decoupler and the latter, in turn, uncoupled by way of an additional friction-locked switching element an additional decoupler.
A transmission device is, in each case, connected to an output of a vehicle drive train, where with an engaged switching element that is arranged between the internal combustion engine and the electric engine and with an engaged switching element that is provided between the electric engine and the transmission device, a vehicle can be driven by the internal combustion engine alone or in combination with the electric machine engine. By engaging only the switching element that is arranged between the electric engine and the transmission device, a vehicle can be driven soley by the electric engine or by braking energy that is recuperable via the electric engine, which is then driven by a generator.
The previously described hybrid systems are used in connection with automated transmissions and in combination with automatic transmissions. Particularly in the case of use in automatic transmissions, a switching element of the automatic transmission is ideally located between the electric engine and the transmission device. A torque converter, provided as a startup device for internal combustion engine startup procedures is, in hybrid drives, often replaced by the switching element arranged between the internal combustion engine and the electric engine or between the electric engine and the transmission device.
The different assemblies in hybrid motor vehicle drive trains are subjected to considerable thermal stresses during critical operating states because, particularly the switching elements between the internal combustion and electric engines and the transmission device must be transferred in a slipping state with high rotational speed differences and with high torque applying to them at the same time into an engaged operating state. This is the case when a vehicle, due to a low charge condition of electrical storage units assigned to the electric engine, has to be started using the internal combustion engine or a clutch configured as a switching element for vibrationally disengaging the internal combustion engine, has to be operated in a slipping state.
In order to reduce the high thermal stresses occurring in the previously described switching elements, the switching elements are usually wet multi-plate clutches of disc brakes, which are cooled by a cooling oil volume flow. In order to adjust the cooling of the switching element to the changing requirements during different operating states of a vehicle drive train, there is an attempt to vary the coolant volume flow that is supposed to be supplied to the switching elements at any given time by way of a predefined strategy subject to operating state.
There is no satisfactory representation capacity with conventional hydraulic systems with electrohydraulic transmission controllers of strategy-compatible cooling systems, of switching elements of drive trains or hybrid drive trains of motor vehicles, as known from DE 198 58 543 A1 or from DE 10 2005 012 586 A1.
This results from the fact that in order to adequately cool the switching elements that are under great thermal stress, in addition to the hydraulic transmission systems, there must also be hydraulic cooling systems with their own coolant circulation and their own coolant pump, which exhibit complex construction, require a large installation space and have a high dead weight, and which are also characterized by a great control and regulation complexity which, among other things, results in high cost.
The present invention is therefore based on the task of providing an electrohydraulic transmission control, a transmission device and a motor vehicle, which reduce thermal stresses on assemblies of a motor vehicle drive train over the entire operating range of a motor vehicle drive train in a simple and cost-effective way.
This task is performed with an inventive electrohydraulic transmission controller and transmission device of a motor vehicle drive train or with a vehicle drive train.